Pacific Gas and Electric Co. knew in 2008 that the San Bruno gas line that later exploded and the network of smaller pipes it fed had multiple potentially at-risk welds, but decided to spike the system's pressure so it could avoid the possibility of costly inspections, according to a company memo turned over to federal investigators.

The memo said portions of the transmission pipeline running through San Bruno and "numerous" feeder lines had welds that the federal government considered to be at risk of failure because of their age or historic reputation for unreliability. Boosting the pressure temporarily on the San Bruno line was a way to get around testing the welds and preserve its legal capacity, the memo said.

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When the line running through San Bruno exploded Sept. 9, killing eight people and leveling 38 homes, the rupture happened at a poorly constructed weld that could have been detected had PG&E inspected the pipe using high-pressure water. The company avoided such tests before last year and inspected the San Bruno pipe using a less costly method best suited to finding corrosion.

Experts said the newly revealed PG&E memo could be a key piece of evidence in the San Bruno investigation, because it indicates that the company feared that the pipeline running through San Bruno was vulnerable and its welds could fail - yet sought to avoid a potential fix.

'Gaming the system'

"They appear to be gaming the system," said pipeline safety expert Richard Kuprewicz of Redmond, Wash., who has followed the San Bruno case and is a technical adviser to the federal government on pipeline issues.

"They're gaming their decision process so they didn't have to do what they were supposed to and what they are required to do by the intent of the regulations," Kuprewicz said. "You are supposed to be identifying the threats, not ignoring them."

Asked about the 2008 memo, PG&E spokesman David Eisenhauer said Friday, "We've openly acknowledged our operations were not what they should have been, and we are working to fix that. Among many other things, we have a new EVP (executive vice president) of gas operations with 30 years' experience in improving some of the nation's oldest gas systems, we are bringing in dozens of new engineers and are putting into place stronger standards."

The issue centers on PG&E's former practice of intentionally increasing pressure to legal maximums for at least two hours on a dozen or more of its older gas transmission lines, including the pipeline known as Line 132 that runs from Milpitas up the Peninsula and through San Bruno.

'Wrong-headed' tactic

Under federal rules, if pressure on a pipe accidentally surges beyond a certain threshold - the highest level at which the line ran in the five years before it fell under the inspection law - an operator must inspect the pipe's welds for possible damage.

For PG&E, such a test would typically involve using high-pressure water. The company has said such tests can cost as much as half a million dollars per mile.

When The Chronicle reported on PG&E's pipe-spiking practice after the San Bruno explosion, the company said it had believed the increases were needed to avoid having pipelines' legal maximum pressures reduced. It also discontinued the practice.

Richard Clark, then the head of consumer protection and safety at the California Public Utilities Commission, criticized the spikings at a federal hearing in March as a "wrong-headed approach to safety," and federal officials said PG&E had misinterpreted the law - that such spikes were not needed to maintain a pipe's legal pressure cap.

Feds taking a look

The intentional increases have caught the attention of the National Transportation Safety Board, which is trying to determine the cause of the San Bruno blast. Investigators say that among the factors they are looking into are the two increases that PG&E conducted on Line 132 and its feeder system, in 2003 and 2008.

PG&E provided the federal agency with few documents explaining how it devised the pressure-increase program, saying it had believed it could dispose of them after three months.

One document that did survive concerned the 2008 pressure increase. Dated Dec. 3 of that year, it was an internal authorization form approved through PG&E's chain of command, explaining the pressure increase planned for the San Bruno line six days later.

Pipeline's 'problem'

The PG&E employee who wrote the document noted that the legal maximum pressure on Line 132 was 400 pounds per square inch. But the company normally kept the pressure at 375 pounds, because the pipe was connected in the South Bay to weaker lines. The company believed that if it didn't run the line at its 400-pound legal cap once every five years, that cap would be reduced.

PG&E's plan, therefore, was to isolate the San Bruno line from the weaker pipes for a few hours and boost its pressure to 400 pounds.

The authorization, or "clearance," was prepared by Todd Arnett, a senior gas transmission engineer. It touched on what Arnett called a "problem" for Line 132.

Federal rules define a "manufacturing threat" as certain kinds of problematic welds, found on older, urban gas transmission lines that have not been pressure-tested.

Many of PG&E's untested lines, including the one that ruptured in San Bruno, have low-frequency electric resistance welds, which the federal government says have contributed to more than 100 pipeline failures nationwide. The weld that failed in the San Bruno blast, however, was not of that variety. Tests showed it had been poorly constructed, extending only halfway through the pipe wall.

Arnett's memo does not indicate what kinds of problem welds were suspected of lurking on Line 132 and its feeder lines, or where.

Feeder-line concerns

The document, which PG&E provided to investigators in March but was only recently disclosed by federal officials, is the first public indication that PG&E had concerns about Line 132's feeder lines. Those are high-pressure mains, running off a larger line, that distribute gas into residential neighborhoods.

It is not clear how many distribution lines PG&E believed had manufacturing threats or potential weld flaws. But Arnett's memo said valves leading to a total of four feeder lines in the Peninsula division had to be opened during the Line 132 pressure increase and that the lines "must see 400 psi."

Spiking unnecessary

Arnett's memo said that if PG&E didn't boost pressure promptly on Line 132 and the feeder lines to 400 pounds, "then the system would not be able to operate up to 400 without significant additional integrity verification work" - high-pressure water testing.

The increase was carried out on Dec. 9, 2008, and the pressure actually topped out at slightly above the 400-pound legal cap. Officials with the federal Pipeline and Hazardous Materials Safety Administration said this year that the spiking was unneeded and, because the pressure exceeded the legal maximum during the process, the increase itself should have initiated water-pressure inspection tests on Line 132.

Post-blast changes

Since the September blast in San Bruno, PG&E has cut the pressure on Line 132 and the distribution lines it serves by 20 percent. It says much of the line and distribution network will operate at half its pre-blast pressure cap - a new peak of 200 pounds per square inch - once all of it is back in service.

The cut in pressure did not give experts much comfort.

"You have such a comedy of errors here, it is difficult to focus on one area," said Ken Kraska, a metallurgical expert who has worked for utilities and now is a private consultant.

"At one time, I would have said this is shocking and stunning," Kraska said. "But at this point, based on what we have learned, this is ordinary business for them. The fact of the matter is, this is the standard way of doing things. They don't seem to know what they are doing."